The present invention is directed to an electrochemical sensor involving an electrode and a coating that surrounds the electrode, the coating comprising a structural component, a water immiscible solvent, a resistance decreasing component, and an ion exchange component, wherein the coating selectively partitions an electrochemically active drug from a fluid or vapor sample whereby an electrochemical signal within the coating can be measured using the electrode. Devices and methods for using this electrochemical sensor are also disclosed.
